1. Field of the Invention
The present invention relates to a microinjection device and a microinjection method.
2. Description of the Related Art
In the fields of biology and medicine, development of new drugs and the like requires observation of reaction to a reaction solution, cell cultivation in a culture medium, and chemical injection into a cell. Japanese Patent Application Laid-Open No.2004-081084, for example, discloses a microinjection technology to drop or inject a minute-quantity of solution such as a chemical into a culture medium or a cell with high accuracy.
Among injection devices available on the market, however, there is no product until today that is characterized in its quantifying ability in introducing a substance to a cell. This is because there is no means in principle other than microinjection for adjusting the introduction amount, and because it is difficult to adopt commonly-used measurement factors such as concentration and electric conductivity due to the volume injected to the cell as small as the order of picolitter (pl) and femtolitter (fl) and also the small flow rate.
The measurement of a substance discharged in minute quantity may be possible with a technique such as radioisotopes. Yet, it is not easy from the aspects of safety and cost to adopt it to an injecting device.
In other fields, for example, an inkjet printer realizes a discharge in units of picolitters. The inkjet printer, however, is clearly different from a microinjection device in that an inkjet printer forms an interface between ink and air.
When a substance is introduced into a cell, a solution of the substance to be introduced is injected into the intracellular fluid so that no interface is formed between the intracellular fluid and the solution of the introduced substance.
As widely known, traction exerts a significant influence upon a substance as small as, or smaller than, micrometers, and the internal pressure of a droplet increases in proportion to the curvature of the droplet.
Thus, even when the volumes of substances are the same, an inkjet printer deals with a far larger pressure by orders of magnitude. It is therefore difficult to apply the same mechanism to the microinjection.
Moreover, the inkjet printer also has a far larger maximum flow rate owing to the function of its actuator. This facilitates the measurement of the total quantity, and also the measurement of an average amount of a single injection.
As described above, the conventional microinjection technologies have a problem in quantification because, without a practical quantitative measuring technique, the adjustment of an injection amount depends on experience and guesswork by referring to the swollenness of a cell or the like.
The microinjection uses a hollow needle whose point has a diameter equal to or smaller than 1 micrometer, so small that it gradually causes clogging around the point and reduces the flow rate. There has been a problem that there is no means to quantitatively correct the flow rate.
Furthermore, the hollow needle is made of glass, and an aqueous solution therein tends to flow backward due to capillary rise. Thus, pressure opposing to the rise needs to be applied all the time. There has been a problem, however, that because the exact threshold of this pressure cannot be found out, there is no choice but to apply an excessive pressure. This causes the injection substance to run off, and there is a possibility that the run-off substance acts on a cell.